An Investigation To Observe The Effects Of Concentration On Rate Of Chemical Reaction.
An Investigation To Observe The Effects Of Concentration On Rate Of Chemical Reaction
Introduction
This is an experiment that will measure the effect of concentration in rate of a chemical reaction. Through the preliminary enquiry I have found that there are four main factors that affect rate of reaction: -
* Temperature
* Concentration
* Surface Area
* Catalysts
The factor that is going to be investigated through this experiment will be concentration. To make this a fair test all the other 3 factors will have to be constants, if there is more than one variable the results will not be accurate. This experiment is based around the 'collision theory'.
The Collision Theory
The collision theory basically states that for a reaction to occur particles must collide. They must also collide hard enough to start a reaction. So this means that if any one of the above four factors is increased then this should increase collisions. For example if we increase temperature in a reaction then we give the particles more kinetic energy, if the particles have more energy they will move faster and collide more often thus increasing the rate of the reaction.
In this investigation the reaction that will be used is the reaction of calcium carbonate (CaCO3) with hydrochloric acid (HCl), this reaction will produce carbon dioxide (CO2), water (H2O) and calcium chloride (CaCl2), as shown below:
calcium carbonate + hydrochloric acid + + water
CaCO3(s) + 2HCl(l) CO2(g) + CaCl2(aq) + H2O(l)
Plan
WATER (cm3)
HYDROCHLORIC ACID (cm3)
0
0
9
8
2
7
3
6
4
5
5
4
6
3
7
2
8
9
0
0
In this investigation the only variable will be concentration of hydrochloric acid, everything else will be a constant, temperature, surface area and the amount of chemicals. The reaction stated above will be carried out with different concentrations of hydrochloric acid. The different concentrations will be obtained by mixing water with, hydrochloric acid of concentration 2 molar, there will ...
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0
0
9
8
2
7
3
6
4
5
5
4
6
3
7
2
8
9
0
0
In this investigation the only variable will be concentration of hydrochloric acid, everything else will be a constant, temperature, surface area and the amount of chemicals. The reaction stated above will be carried out with different concentrations of hydrochloric acid. The different concentrations will be obtained by mixing water with, hydrochloric acid of concentration 2 molar, there will be 11 concentrations that have a volume of 10cm3 each, this amount of values will provide sufficient results to draw accurate conclusion. The concentrations will be made using ratios of acid to water, as shown below:
Each of the above concentrations will be reacted with 3 grams of precipitated calcium carbonate for 20 seconds, this time period will provide sufficient time to produce an acceptable amount of carbon dioxide. The 3 grams of calcium carbonate will be placed in a conical flask, the hydrochloric acid will then be poured into the flask and a bung with a rubber pipe will be placed in the top. It is essential that this bung is placed in quickly after the acid has been poured in, to prevent gas from escaping. Precipitated calcium carbonate is used opposed to chips because the surface area is more constant in powder. The gas produced (carbon dioxide) in this 20 seconds will be collected and measured using a water bath. Below is a diagram showing how the experiment will be set out.
The whole experiment will be conducted 4 times. This helps to make the test fair and eliminate anomalous results, by averaging. Speed is essential in this experiment, because in the time it takes to place the bung in the conical flask gas will escape, this could prevent the results from being reliable. Also safety precautions should be taken when around acidic chemicals, safety goggles should be worn.
Prediction
I predict that the higher the concentration of hydrochloric acid, the faster the reaction will take place. I believe this because if the concentration of hydrochloric acid molecules is great the there will be a greater chance of collision between a hydrochloric acid molecule and a calcium carbonate molecule, causing a greater rate of reaction. I also believe that if the concentration of hydrochloric acid is doubled, the amount of carbon dioxide produced in 20 seconds will also be doubled. This is because there will be twice as many hydrochloric acid molecules the chance of a collision will be twice as big. I also predict that the reaction will be quick at first and then slow down as the reactants get used, this is because as there becomes fewer reactants the chance of a collision will reduce thus causing the reaction to slow down. I think that this will produce a graph as shown below:
Results
Ratio water: acid
Test 1
Amount
of CO2
Produced
Test 2
Amount
of CO2
Produced
Test 3
Amount
of CO2
Produced
Test 4
Amount
of CO2
Produced cm3
Average Result
0 : 0
0
0
0
0
0.00
9: 1
3
2
2
2.00
8: 2
4
5
8
6
5.75
7: 3
9
0
4
2
1.25
6:4
4
21
6
5
6.50
5: 5
37
34
32
31
33.50
4: 6
39
45
44
42
42.50
3: 7
52
56
58
48
53.50
2: 8
64
69
74
68
68.75
: 9
79
89
86
82
84.00
0: 10
91
96
93
96
94.00
__ = anomalous result
For graphs turn to back.
Conclusion
The results clearly show that the concentration of hydrochloric acid has an effect on the reaction rate in this reaction. The effect is that the rate of reaction increases as the concentration of the acid increases. During the reactions it was observed that the reaction was very quick at first, but then after a few seconds it got much slower. This was due to the reactants being used up. From the results the conclusion can be drawn that the greater the concentration, the greater the rate of the chemical reaction. This is so because, when the concentration of hydrochloric acid is great the chance of a collision with a calcium carbonate molecule will increase thus causing the rate of reaction to increase, all of the graphs support this. As the reactants get used the rate of the reaction slowed down, this happens because the chance of a collision reduces as there becomes fewer molecules of calcium carbonate and of hydrochloric acid to react.
The prediction I made was accurate in stating the outcome of the experiment, apart from one aspect. I stated that if the concentration of hydrochloric acid were doubled, the amount of carbon dioxide produced would be twice as much. None of the results support this statement, because if you look at the values of carbon dioxide produced from the concentration ratios 5:5 and 0:10. The value for 0:10 is not twice the value of 5:5 in any case, if my statement was true then the value of 0:10 would be close to twice the amount of 5:5. I believe that if the chemicals were left to react for longer then the statement might have been correct.
Evaluation
I believe that the results and measurements obtained from this experiment were sufficient to allow me to draw an effective conclusion. Although I do not believe that the measurements were sufficiently accurate, this is due to limited equipment and uncontrollable atmospheres, such as the air pressure and room temperature. The experiments were not all conducted on the same day, so it is extremely likely that the values for things such as room temperature were different, and this would have a direct effect on the results. There was one anomaly that stood out, this was the reading from test 1 that is highlighted in the table and circled on the graph. This anomaly could be due to the inconsistency in the delay from when the hydrochloric acid is poured into the flask and the bung being placed into the top of the flask. This could have a fairly big effect on the results because most gas is produced at the start of the reaction. Measuring the mass of the solution instead of collecting the gas could perhaps eliminate this problem. Although the results may not have been extremely reliable, they were fairly consistent as we can see from the graphs. The graphs certainly follow a positive trend.
Other investigations that could be done following on from this one would be investigating the other factors that affect rate of reaction, such as temperature, surface area and catalyst.
